Preparation for production of formic acid formates

ABSTRACT

A process is described for preparing acid formates in which methyl formate is reacted with water and a basic compound having a pK a  of the conjugate acid of the corresponding dissociation state of ≧3 measured at 25° C. in aqueous solution, the methanol formed is separated off and, optionally, the desired acid content is set by adding formic acid.

The present invention relates to a process for preparing acid formates.

Acid formates have an antimicrobial activity and are used, for example,for preserving and acidifying materials of vegetable and animal origin,for example grasses, agricultural products or meat, for treatingbiowastes, or as an additive for animal nutrition.

Acid formates and preparation methods for these have long been known,thus, Gmelins Handbuch der anorganischen Chemie [Gmelin's Handbook ofInorganic Chemistry], 8^(th) edition, Number 21, pages 816 to 819,Verlag Chemie GmbH, Berlin 1928 and Number 22, pages 919 to 921, VerlagChemie GmbH, Berlin 1937, describes the synthesis of sodium diformate orpotassium diformate by dissolving sodium formate or potassium formate informic acid. The crystalline diformates may be obtained by lowering thetemperature and evaporating off excess formic acid.

DE 424017 teaches the preparation of sodium acid formates having varyingacid content by introducing sodium formate into aqueous formic acid inan appropriate molar ratio. By cooling the solution the correspondingcrystals are obtained.

According to J. Kendall et al., Journal of the American ChemicalSociety, Vol. 43, 1921, pages 1470 to 1481, potassium acid formates areobtainable by dissolving potassium carbonate in 90% strength formicacid, forming carbon dioxide. The corresponding solids can be obtainedby crystallization.

GB 1,505,388 discloses the preparation of acid carboxylate solutions bymixing the carboxylic acid with a basic compound of the desired cationin aqueous solution. Thus, for example, in the preparation of acidammonium carboxylate solutions, ammonia water is used as basic compound.

U.S. Pat. No. 4,261,755 describes the preparation of acid formates byreacting an excess of formic acid with the hydroxide, carbonate orbicarbonate of the corresponding cation.

WO 96/35657 teaches the preparation of products which contain disalts offormic acid by mixing potassium, sodium, cesium or ammonium formate,potassium, sodium or cesium hydroxide, carbonate or bicarbonate, orammonia with optionally aqueous formic acid, subsequently cooling thereaction mixture, filtering the resultant suspension and drying theresultant filter cake and recirculating the filtrate.

A disadvantage of the abovementioned processes is that for each mole offormate formed by reaction with the basic compounds, one mole of formicacid is consumed and, as a result, based on the entire added-valuechain, the processes are complex, costly and energy consuming.

It is an object of the present invention, therefore, to provide aprocess which no longer has the abovementioned disadvantages, whichmakes it possible to prepare acid formates on an industrial scale inhigh yield, with simultaneous high flexibility with respect tocomposition and using readily accessible raw materials and permitssimple process design with low capital costs.

We have found that this object is achieved by a process for preparingacid formates which comprises reacting methyl formate with water and abasic compound having a pK_(a) of the conjugate acid of thecorresponding dissociation state of ≧3 measured at 25° C. in aqueoussolution, separating off the methanol formed and, optionally, settingthe desired acid content by adding formic acid.

Acid formates are compounds and mixtures which contain formate anions(HCOO—), cations (M^(X+)) and formic acid (HCOOH). They can be presenttogether in the form of a solid or a liquid and may contain othercomponents, for example other salts, additives or solvents, for examplewater. Generally, the acid formates can be represented by the formulaHCOO—M^(X+) _(1/x) *yHCOOH  (I),where M is a monovalent or polyvalent inorganic or organic cation, x isa positive number and indicates the charge of the cation and y is themolar fraction of formic acid based on the formate anion. The molarfraction of formic acid based on the formate anion y is generally from0.01 to 100, preferably from 0.05 to 20, particularly preferably from0.5 to 5, and in particular from 0.9 to 3.1.

The nature of the inorganic or organic cation M^(X+) is not critical inprinciple provided that it is stable under the conditions under whichthe acid formate is to be handled. This is also taken to mean, forexample, stability toward the reducing formate anion. Possible inorganiccations are the monovalent and/or polyvalent metal cations of metalsfrom groups 1 to 14 of the Periodic Table of the Elements, for examplelithium (Li⁺), sodium (Na⁺), potassium (K⁺), cesium (Cs⁺), magnesium(Mg²⁺), calcium (Ca²⁺), strontium (Sr²⁺) and barium (Ba²⁺), preferablysodium (Na⁺), potassium (K⁺), cesium (Cs⁺) and calcium (Ca²⁺). Possibleorganic cations are unsubstituted ammonium (NH₄ ⁺) and ammoniumsubstituted by one or more carbon-containing radicals which canoptionally also be bound to one another, for example methylammonium,dimethylammonium, trimethylammonium, ethylammonium, diethylammonium,triethylammonium, pyrollidinium, N-methylpyrroldinium, piperidinium,N-methylpiperidinium or pyridinium.

A carbon-containing organic radical is an unsubstituted or substitutedaliphatic, aromatic or araliphatic radical having from 1 to 30 carbons.This radical can contain one or more heteroatoms, such as oxygen,nitrogen, sulfur or phosphorus, for example —O—, —S—, —NR—, —CO—, —N═,—PR— and/or —PR₂ and/or can be substituted by one or more functionalgroups which contain, for example, oxygen, nitrogen, sulfur and/orhalogen, for example by fluorine, chlorine, bromine, iodine and/or acyano group (the radical R in this case is also a carbon-containingorganic radical). The carbon-containing organic radical can be amonovalent or polyvalent, for example divalent or trivalent, radical.

To prepare the acid formates, in the inventive process, methyl formateis reacted with water and a basic compound having a PK_(a) of theconjugate acid in the corresponding dissociation state of ≧3, preferably≧3.5, particularly preferably ≧9 and very particularly preferably ≧10,measured at 25° C. in aqueous solution. The basic compound can beinorganic or organic. The basic compound can be a salt or a covalentcompound. The conjugate acid of the corresponding dissociation state inthis case is the acid formed by formal addition of a proton (H⁺).

In the event that the basic compound is a salt, this can in general berepresented by the formulaM^(x+) _(a)A^(a−) _(x)  (II),where M and x have the meaning specified under (I) and A is an inorganicor organic anion having the charge “a−”. The conjugate acid of thecorresponding dissociation state thus corresponds to HA^((a−1)−). Thecorresponding dissociation equation, which defines the pK_(a) to beused, is as follows

In the event that the basic compound is a covalent compound B, thedissociation equation which defines the PK_(a) to be used is as follows

Examples of suitable basic compounds are the salts M^(x+) _(a)A^(a−)_(x) (II), where M^(x+) is a monovalent or polyvalent metal cation of ametal as described above and A^(a−) is an anion as listed in Table 1aand the covalent compounds B listed in Table 1b.

TABLE 1a Possible anions A^(a−) of suitable basic compounds and PK_(a)S(measured at 25° C. in aqueous solution) of the conjugate acids of thecorresponding dissociation states. Anions A^(a−) Conjugate acid pK_(a)Hydroxide (OH⁻) Water (H₂O) 14.0 Carbonate (CO₃ ²⁻) Hydrogen carbonate(HCO₃ ⁻) 10.3 Hydrogen carbonate (HCO₃ ⁻) Carbonic acid (H₂CO₃) 6.4Borate (BO₃ ³⁻) Hydrogen borate (HBO₃ ²⁻) >14 Hydrogen borate (HBO₃ ²⁻)Dihydrogen borate (H₂BO₃ ⁻) >14 Dihydrogen borate (H₂BO₃ ⁻) Boric acid(H₃BO₃) 9.3 Phosphate (PO₄ ³⁻) Hydrogen phosphate (HPO₄ ²⁻) 12.3Hydrogen phosphate (HPO₄ ²⁻) Dihydrogen phosphate (H₂PO₄ ⁻) 7.2 FormateFormic acid 3.8 Acetate Acetic acid 4.8 Propionate Propionic acid 4.9Oxalate (C₂O₄ ²⁻) Hydrogen oxalate (HC₂O₄ ⁻) 4.2 2-Ethylhexanoate2-Ethylhexanoic acid >4 (C₄H₉—CH(C₂H₅)—COO⁻) (C₄H₉—CH(C₂H₅)—COOH)

TABLE 1b Possible covalent bases B as suitable basic compounds andpK_(a)s (measured at 25° C. in aqueous solution) of the conjugate acidsof the corresponding dissociation states. Covalent base B Conjugate acidpK_(a) Ammonia Ammonium  9.3 Methylamine Methylammonium 10.6Dimethylamine Dimethylammonium 10.7 Trimethylamine Trimethylammonium 9.8 Ethylamine Ethylammonium 10.7 Diethylamine Diethylammonium 11.0Triethylamine Triethylammonium 10.8 Pyrollidine Pyrollidinium 11.3N-Methylpyrroldine N-Methylpyrroldinium 10.3 Piperidine Piperidinium11.1 N-Methylpiperidine N-Methylpiperidinium 10.1 Pyridine Pyridinium 5.3

Preferably, in the inventive process, the basic compound used is lithiumhydroxide, lithium hydrogen carbonate, lithium carbonate, lithiumformate, sodium hydroxide, sodium hydrogen carbonate, sodium carbonate,sodium formate, potassium hydroxide, potassium hydrogen carbonate,potassium carbonate, potassium formate, ammonium carbonate, ammoniumhydrogen carbonate and/or ammonia, particularly preferably sodiumhydroxide, sodium hydrogen carbonate, sodium carbonate, sodium formate,potassium hydroxide, potassium hydrogen carbonate, potassium carbonate,potassium formate and/or ammonia, and particularly preferably sodiumhydroxide, sodium carbonate, sodium formate, potassium hydroxide,potassium carbonate and/or potassium formate, in particular sodiumhydroxide, sodium formate, potassium hydroxide and/or potassium formate.

The manner in which the basic compounds are added is generally notcritical in the inventive process. They can be added in solid, liquid orgaseous form, as pure substance, as mixture of substances or assolution. Examples which may be mentioned are addition in the form ofaqueous solutions (for example aqueous solutions of the alkali metalsalts or ammonia water), in the form of solid compounds (for examplepowders of the alkali metal salts), in the gaseous state (for examplegaseous ammonia). Preference is given to addition in the form of theiraqueous solutions.

The sequence in which the starting materials are added is also ingeneral not critical in the inventive process. Thus, it is possible, forexample, to introduce first the basic compound in solid or liquid form(for example as aqueous solution) and then to introduce the methylformate in the liquid or gaseous state with stirring. It is alsopossible to introduce first the methyl formate in liquid form and thento add the basic compound. In addition, obviously, the startingmaterials can also be added in parallel in the desired ratio.

The molar ratio of methyl formate to the basic compound is generally notcritical for the process. Generally, at least as much methyl formate isused with respect to the basic compound so that, on the basis of thereaction stoichiometry, all of said basic compound is converted intoformate. The critical parameter of this is what is termed the molarequivalent of the basic compound, which must take into account in thiscase all dissociation states which lead by addition of protons toconjugate acids which have a PK_(a) of ≧3, measured at 25° C. in aqueoussolution. Thus, for example, a methyl formate/potassium hydroxide molarratio of 2.0 leads to the formation of potassium diformate HCOOK*HCOOH,since 1 mol of KOH corresponds to 1 molar equivalent:

A methyl formate/potassium carbonate molar ratio of 2.0, in contrast,leads to the formation of potassium formate HCOOK, since 1 mol of K₂CO₃corresponds to 2 molar equivalents:

Depending on the molar ratio employed of methyl formate to the molarequivalent of the basic compound, the reaction product obtained is amixture containing formate HCOO—M^(x+) _(1/x) (without excess of formicacid) or acid formate (I) HCOO—M^(x+) _(1/x)*y HCOOH and methanol, ifappropriate water and if appropriate reaction products of the basiccompound.

The methanol formed is separated off in the inventive process from theresultant reaction mixture, in which case, if appropriate, othercomponents, for example formic acid, can be added to this reactionmixture in advance. The methanol can be removed, for example, by thecustomary known processes, for example by evaporation. In theevaporation of methanol, it is also possible to separate off conjointlya portion of any water present, if appropriate all of the water.Preference is given to evaporating methanol without significant amountsof water, since in this case methanol is predominantly obtained ascondensate, which can, for example, be reused in the synthesis of methylformate by carbonylation. A further possible process for separating offthe methanol formed is crystallization and removal of the formateHCOO—M^(x+1) _(1/x) or the acid formate (I) HCOO—M^(x+) _(1/x) ^(*)yHCOOH, in which a mother liquor containing methanol and formate or acidformate is obtained. By subsequent distillation, methanol can beobtained from this mother liquor. The remaining bottom phase product isadvantageously recirculated to the formate synthesis stage.

If in the said reaction a product having a lower formic acid contentthan desired was obtained (for example formate alone, without an excessof formic acid), formic acid can be added subsequently to the mixtureobtained. Generally it is advantageous in this case first to remove themethanol formed (for example by distillation) and then, by adding formicacid, to set the desired acid content of the acid formate.

If the reaction between the methyl formate, the water and the basiccompound is carried out in such a manner that firstly only formate(without excess of formic acid) or formate with a very slight excess offormic acid is formed, the desired acid content of the acid formate tobe prepared must be set by adding formic acid. The addition can be made,as mentioned above, before or after separating off the methanol.

Preference is given in the inventive process to the preparation of acidformates in which the methyl formate is reacted with water and a basiccompound, as defined above, directly to form acid formates (I) and themethanol formed is separated off. In this preferred variant, subsequentsetting of the desired acid content by subsequent addition of formicacid is generally no longer necessary.

In the inventive process, generally a molar ratio of methyl formate“n(methyl formate)” in the fresh feed to the molar equivalent of thebasic compound “n′ (basic compound)” in the fresh feed, taking intoaccount all dissociation states which lead, by addition of protons, toconjugate acids which have a pK_(a) of ≧3, measured at 25° C. in aqueoussolution, of$\frac{n\left( {{methyl}\quad{formate}} \right)}{n^{\prime}\left( {{basic}\quad{compound}} \right)}$of from 0.5 to 100 is used. Preferably, said molar ratio is from 1.0 to10, particularly preferably from 1.1 to 20, very particularly preferablyfrom 1.5 to 6, and in particular from 1.9 to 4.1. The term “fresh feed”is the starting material stream fed externally to the production plantfor preparing the acid formates without taking into account anyrecirculated components.

The amount of water to be used in the inventive process can vary over abroad range. Generally, in the inventive process, in the reaction, aconcentration of water of from 0.1 to 95% by weight, preferably from 5to 80% by weight, and particularly preferably from 10 to 70% by weight,in the reaction apparatus is used.

The amount of freshly fed water generally corresponds to the amountstoichiometrically required for the reaction. The inventive process isgenerally carried out at a temperature of from 0 to 150° C., preferablyfrom 30 to 120° C., and particularly preferably from 50 to 80° C. Whenthe inventive process is carried out, the pressure is generally from0.05 to 1 MPa absolute, preferably from 0.08 to 0.5 MPa absolute, andparticularly preferably from 0.09 to 0.15 MPa absolute.

Reaction apparatuses which can be used are in principle all reactionapparatuses which are suitable for reactions in the liquid phase.Examples are stirred tanks and jet loop reactors.

The methanol formed is separated off in the inventive process preferablyby evaporation from the reaction mixture. Suitable methods forevaporation are distillation and stripping. In distillation theresultant reaction mixture is generally transferred to a batchwise,semicontinuous or continuous column and distilled there. However, it isalso possible to evaporate off the methanol from the reaction apparatusafter the reaction. In this case the reaction apparatus isadvantageously fitted with a distillation attachment. In the case ofstripping, a stripping gas is passed through the reaction mixture.Suitable stripping gases are in principle all gases which are inert withrespect to the reaction mixture, for example air, nitrogen, oxygen,noble gases or mixtures thereof.

If it is intended to prepare aqueous solutions of the acid formates,generally, after the methanol removal, the desired water content is set.This is achieved by supplying or distilling off water.

In a preferred embodiment of the inventive process, the mixture obtainedafter methanol removal is cooled for crystallization and theprecipitated acid formates are separated off. Said crystallization isgenerally carried out at a temperature in the range from −20° C. to +30°C., and preferably from 0° C. to 30° C.

Generally, the amount of product crystallized out increases withdecreasing temperature. Crystallization can in principle be carried outin all known apparatuses therefor. It can proceed, for example,following the methanol removal, directly in the reaction apparatus, inthe column bottom phase, in a further stirred tank or in a crystallizer.Said embodiment can be used particularly advantageously for separatingoff acid formates which are crystallizable in the desired composition.Relevant examples are potassium diformate (HCOOK*HCOOH), sodiumdiformate (HCOONa*HCOOH), sodium tetraformate (HCOONa*3 HCOOH) ormixtures thereof.

The crystallized formates or acid formates are generally removed byconventional and known methods, for example by filtration orcentrifugation.

The mother liquor obtained after separating off the acid formates ispreferably reused in the reaction of methyl formate with water and thebasic compound.

The reaction of methyl formate with water and the basic compound, theremoval of methanol and the isolation of the acid formates can becarried out batchwise, semicontinuously or continuously. Preferably,said reaction and removal of methanol are carried out continuously.

Particularly preferably, in the inventive process potassium diformate(HCOOK*HCOOH), sodium diformate (HCOONa*HCOOH), sodium tetraformate(HCOONa*3 HCOOH) or mixtures thereof, and in particular potassiumdiformate are prepared.

The acid formates are generally prepared in the form of their solutionsor crystalline as solids. To them may be added other components, forexample other formate salts. In the case of the crystalline acidformates, it is generally advantageous for storage, transport and use tocompress these together with a dessicant, for example silicates orstarch, to give a particulate compactate or various shaped bodies, forexample tablets or spheres.

In addition, the invention relates to the use of the inventivelyprepared acid formates for preserving and/or acidifying materials ofplant or animal origin. Examples are the use of acid formates forpreserving and acidifying grass, agricultural crops, fish and fishproducts and meat products, as are described, for example, in WO97/05783, WO 99/12435, WO 00/08929 and WO 01/19207.

Furthermore, the invention relates to the use of the inventivelyprepared acid formates for treating biowastes. The use of acid formatesfor treating biowastes is described, for example, in WO 98/20911.

The invention also relates to the use of the inventively prepared acidformates as an additive in animal nutrition and/or as growth promotersfor animals, for example breeding sows, fattening pigs, poultry, calvesand cows. Said use is described, for example, in WO 96/35337. Preferenceis given to the use of the inventively prepared potassium acid formates,in particular potassium diformate, as an additive in animal nutritionand/or as growth promoters for animals, in particular for breeding sowsand fattening pigs.

In addition, the invention relates to the use of the inventivelyprepared acid formates for preserving and/or acidifying materials ofplant or animal origin, for treating biowastes and/or as an additive inanimal nutrition.

Particular preference is given to the use as an additive in animalnutrition. Preferred acid formate-containing products are the mixturesbelow:

Mixture 1 Mixture 2 (% by weight) (% by weight) Potassium diformate 20to 60 60 to 99 Sodium diformate/tetraformate 20 to 50 — Calcium formate 0 to 25  0 to 28 Desiccant (silicate or starch) 0 to 4 0 to 4 Water 0to 5 0 to 5

Very particular preference is given to the use of the inventivelyprepared potassium diformate in animal nutrition in the form of aproduct of composition 98.0±1% by weight potassium diformate, 1.5±1% byweight silicate and 0.5±0.3% by weight water.

In a general embodiment for the continuous preparation of potassiumdiformate, an aqueous potassium hydroxide and/or potassium formatesolution is placed in a reactor (for example a stirred tank), thesolution is heated to the desired temperature of preferably from 50 to80° C. and methyl formate introduction is started, with stirring. Theamount of water present was set in such a manner that, under thereaction conditions, all of the potassium salt used and also thepotassium formate formed are present in dissolved form. After an amountof 1 mol of methyl formate, based on 1 mol of potassium salt used, hasbeen added, introduction of further potassium salt solution is started,in parallel with the feed of methyl formate. The stoichiometry betweenmethyl formate and the potassium salt is then further 1:1. After thedesired liquid level in the reactor has been achieved, transfer to adistillation column is started. There, after the operating point hasbeen reached, methanol is distilled off overhead continuously. Theresultant methanol can, for example, be reused in the synthesis ofmethyl formate via carbonylation. The resultant bottoms discharge ispassed into a crystallization vessel, an equimolar amount, based onpotassium formate, of formic acid is added with stirring, and themixture is cooled to a temperature of from 10 to 25° C., potassiumdiformate precipitating out. The precipitated potassium diformate isseparated off via filtration or centrifugation and fed to a drier. Themother liquor, which still contains further dissolved potassium formateand formic acid, is continuously recirculated to the reaction apparatus.

In a preferred embodiment for the continuous preparation of potassiumdiformate, an aqueous potassium hydroxide and/or potassium formatesolution is placed in a reactor (for example a stirred tank), thesolution is heated to the desired temperature of preferably from 50 to80° C. and methyl formate introduction is started, with stirring. Theamount of water present was set in such a manner that, under thereaction conditions, all of the potassium salt used and also thepotassium formate formed are present in dissolved form. After an amountof 2 mol of methyl formate, based on 1 mol of potassium salt used, hasbeen added, introduction of further potassium salt solution is started,in parallel with the feed of methyl formate. The stoichiometry betweenmethyl formate and the potassium salt is then further 2:1. After thedesired liquid level in the reactor has been achieved, transfer to adistillation column is started. There, after the operating point hasbeen reached, methanol is distilled off overhead continuously. Theresultant methanol can, for example, be reused in the synthesis ofmethyl formate via carbonylation. The resultant bottoms discharge ispassed into a crystallization vessel and cooled to a temperature of from10 to 25° C., potassium diformate precipitating out. The precipitatedpotassium diformate is separated off via filtration or centrifugationand fed to a drier. The mother liquor, which still contains furtherdissolved potassium formate and formic acid, is continuouslyrecirculated to the reaction apparatus.

The inventive process makes it possible to prepare acid formates on anindustrial level in high yield with simultaneously high flexibility withrespect to composition and using readily accessible raw materials with asimple process design and low capital costs. In addition, the processhas the decisive advantage that the formate and, in the preferredembodiment, the formic acid content also, of the acid formate can beproduced directly from methyl formate without the costly andresource-consuming diversion via concentrated formic acid. The inventiveprocess is therefore simple to carry out in processing terms and,compared with the processes involving direct use of concentrated formicacid according to the prior art, has significantly lower capital andenergy costs. In addition, the use of highly alloyed steels is notnecessary, since the acid formates are far less corrosive thanconcentrated formic acid.

EXAMPLES Example 1

50 g (2.78 mol) of water, 10 g of potassium formate containing 2% byweight of water (equivalent to 0.12 mol of potassium formate), 5 g ofpotassium diformate containing 2% by weight of water (equivalent to0.038 mol of potassium diformate) and 10 g (0.17 mol) of methyl formatewere placed in a 400 ml glass autoclave equipped with a gas-introductionstirrer and the mixture was heated at 60° C. for 24 hours. The reactionsolution was then cooled to room temperature to crystallize outpotassium diformate. The potassium diformate which crystallized out wasisolated and dried. From the content of methyl formate in the filtrate,determined quantitatively by gas chromatography, its conversion rate wascalculated as 72%. The filtrate was concentrated completely byevaporation and the sedimented potassium diformate was isolated anddried. Both potassium diformate samples were then combined, weighed andanalyzed for water and potassium contents. A potassium content of 30% byweight and a water content of 2% by weight were found, which correspondsto the composition of potassium diformate having a residual content ofwater of crystallization. Corrected by the amount of potassium formateand potassium diformate used, in total 15.5 g (0.12 mol) of potassiumdiformate were obtained.

Example 2

Example 2 was carried out in a similar manner to Example 1, except forthe amount of potassium diformate used, which was 0.5 g (equivalent to0.0038 mol of potassium diformate). The conversion rate of methylformate was 72%. The mixed sample from the product which wascrystallized out and obtained by evaporative concentration had apotassium content of 30% by weight and a water content of 2% by weight.Corrected by the amount of potassium formate and potassium diformateused, in total 15.5 g (0.12 mol) of potassium diformate were obtained.

Example 3

29.9 g (1.66 mol) of water, 9.3 g of potassium hydroxide (0.17 mol ofpotassium hydroxide) and 20 g (0.33 mol) of methyl formate were placedin a 400 ml glass autoclave equipped with a gas-introduction stirrer andheated at 60° C. for 24 hours. The reaction solution was then cooled toroom temperature to crystallize out potassium diformate. The potassiumdiformate which crystallized out was isolated and dried. From thecontent of methyl formate in the filtrate which was determinedquantitatively by gas chromatography, its conversion rate was calculatedas 92%. The filtrate was concentrated completely by evaporation and thesedimented potassium diformate was isolated and dried. Both potassiumdiformate samples were then combined, weighed and analyzed for water andpotassium content. A potassium content of 30% by weight and a watercontent of 2% by weight were found, which corresponds to the compositionof potassium diformate having a residual content of water ofcrystallization. Corrected by the amount of potassium formate andpotassium diformate used, in total 19.9 g (0.15 mol) of potassiumdiformate were obtained.

Example 4

50 g (0.89 mol) of potassium hydroxide and 10.25 g of water (0.57 mol)were placed in a 400 ml glass autoclave and heated to 60° C. Then, inthe course of 6 hours at 60° C., 107 g (1.78 mol) of methyl formate wereadded. The reaction solution was cooled to room temperature and theliquid discharge was analyzed by gas chromatography. Methyl formate wasno longer detected. The liquid discharge was concentrated to separateoff water and methanol and the potassium diformate was isolated. Theconversion rate of methyl formate was >99%, and the yield of potassiumdiformate was 116 g (0.89 mol). The water content in the potassiumdiformate was 2.0% by weight, and the potassium content was 29.8% byweight.

Example 5

74.8 g (0.89 mol) of potassium formate and 30.0 g of water (1.67 mol)were placed in a 400 ml glass autoclave and heated to 60° C. Then, inthe course of 6 hours at 60° C., 53.5 g (0.89 mol) of ethyl formate wereadded. The reaction solution was cooled to room temperature and theliquid discharge was analyzed by gas chromatography. Methyl formate wasno longer detected. The liquid discharge was concentrated to separateoff water and methanol and the potassium diformate was isolated. Theconversion rate of methyl formate was >99%, and the yield of potassiumdiformate was 116 g (0.89 mol). The water content in the potassiumdiformate was 2.2% by weight and the potassium content was 29.9% byweight.

Example 6

50 g (0.89 mol) of potassium hydroxide and 10.25 g of water (0.57 mol)were placed in a 400 ml glass autoclave and heated to 60° C. Then, inthe course of 6 hours at 60° C., 107 g (1.78 mol) of methyl formate wereadded. The reaction solution was cooled to room temperature and theliquid discharge was analyzed by gas chromatography. Methyl formate wasno longer detected. The methanol was separated off from the liquiddischarge by distillation at atmospheric pressure. On cooling the bottomphase, 21 g of potassium diformate crystallizes out, which was isolatedby filtration. The resultant potassium diformate is characterized by alow water content <2.0% by weight, without additional drying beingperformed. The residual potassium diformate can be isolated byseparating off the water by distillation. The conversion rate of methylformate was >99%, and the yield of potassium diformate was, in total,116 g (0.89 mol).

1. A process for preparing acid formates which comprises reacting methylformate with water and a basic compound selected from the groupconsisting of sodium hydroxide, sodium hydrogen carbonate, sodiumcarbonate, sodium formate, potassium hydroxide, potassium hydrogencarbonate, potassium carbonate, potassium formate and/or ammonia,separating off the methanol formed and, optionally, setting the desiredacid content by adding formic acid.
 2. A process as claimed in claim 1,wherein a molar ratio of methyl formate in the fresh feed to the molarequivalent of the basic compound in the fresh feed, taking into accountall dissociation states which lead, by addition of protons, to conjugateacids which have a pK_(a)≧3, measured at 25° C. in aqueous solution, offrom 1.0 to 10 is used.
 3. A process as claimed in claim 1 wherein, inthe reaction, a concentration of water of from 0.1 to 95% by weight inthe reaction apparatus is used.
 4. A process as claimed in claim 1,wherein the reaction is carried out at a temperature of from 0 to 150°C. and at a pressure from 0.05 to 1 MPa absolute.
 5. A process asclaimed in claim 1, wherein the methanol formed is separated off byevaporation from the reaction mixture.
 6. A process as claimed in claim5, wherein the resultant mixture is cooled and the precipitated acidformates are separated off.
 7. A process as claimed in claim 6, whereinthe mother liquor obtained when the acid formates are separated off isreused in the reacton of methyl formate with water and a basic compound.8. A process as claimed in claim 1, wherein potassium diformate, sodiumdiformate, sodium tetraformate or mixtures thereof are prepared.